The invention relates to a sounding apparatus for pressing a sounding rod into a piece of ground in order to determine the soil properties at various depths, comprising:
a sounding rod which is intended to be pressed into a piece of ground;
first and second clamping members for alternately clamping the sounding rod in place;
first drive means for moving the first clamping member up and down in the longitudinal direction of the sounding rod.
A sounding apparatus of this nature is known from SU-A-476 367. The sounding apparatus described herein comprises a sounding rod with a conical measurement head which is intended to determine soil properties at various depths. In this case, the sounding rod is pressed into a piece of ground in steps (discontinuously). The apparatus comprises a first clamping member which is directly connected to two pistons of a hydraulic system. The pistons are indirectly actuated by means of a gear-rack transmission for each downwards movement. The first clamping member is designed with two tilting bodies which clamp the sounding rod in place during a downwards movement of the first clamping member and release it during an upwards movement. The apparatus furthermore comprises a second clamping member which is designed with two tilting bodies which automatically release the sounding rod during a downwards movement of the sounding rod and clamp it in place in the event of any upwards movement of the sounding rod. The second clamping member is fixedly connected to a frame. The gear wheel comprises a section of approximately a quarter of a circle which is cut out. The hydraulic system is under spring load. Shortly before the end of the downwards movement of the pistons, the cut-out section in the gearwheel comes to lie opposite the rack. This provides the pistons with the freedom to execute an upwards movement under spring load, during which movement the first clamping member automatically moves into an open position. At the same time, the fixedly arranged second clamping member prevents the sounding rod from being able to carry out an undesired movement back upwards. The sounding apparatus is then ready for the next penetration movement.
A drawback of this known sounding apparatus is that it is only able to carry out discontinuous sounding measurements. The penetration movement of the sounding rod into the soil is always interrupted as soon as the pistons have reached their lowest point and have to carry out an upwards movement before the penetration movement can be continued. Waiting each time for the pistons to return to their uppermost point wastes valuable working time. Even more importantly, during each interruption of the sounding measurement, the soil in the area of the sounding rod is given time to settle. Owing to dissipation effects and the build-up of skin friction, the measurement data from a thin layer of soil are lost each time. Furthermore, the structure of the known sounding apparatus is complex
It should be noted that over the course of the years, a number of structures have been designed for carrying out a continuous downwards penetration movement of a sounding rod, using a sounding apparatus. Hitherto, however, no satisfactory solution has been found.
The object of the invention is to overcome the abovementioned drawbacks, and in particular to provide a sounding apparatus which is simple to operate and which can be used to carry out both continuous and discontinuous sounding measurements.
This object is achieved according to the invention by means of a sounding apparatus according to claim 1. According to the invention, the sounding apparatus comprises first and second clamping members which can be separately actuated between a closed position, in which a sounding rod is clamped in place, and an open position, in which a sounding rod is released. First drive means are provided for the first clamping member, while second drive means are provided for the second clamping member. Both the first and the second drive means are able to cause the associated clamping members to carry out upwards and downwards movements. The clamping members and the drive means are connected to control means. The control means are able to cause the clamping members to alternately clamp in place and release, and, by means of activation of the associated drive means, to carry out upwards and downwards movements. Since both clamping members can move up and down in a separately controllable manner and can be activated separately with regard to the clamping function, the sounding apparatus can advantageously be employed in multifunctional mode. In particular, it is possible, according to the invention, to carry out reliable continuous sounding measurements. This will be explained in more detail below. The sounding apparatus according to the invention is suitable to be supported on the ground via a frame, but may advantageously also be mounted on any sounding vehicle, for example a caterpillar vehicle. In addition to continuous sounding, the apparatus may furthermore be used for carrying out discontinuous sounding measurements, for taking soil samples and for drilling. The sounding apparatus is also suitable for carrying out sounding measurements underwater, for example on the sea bed, provided that it is equipped with a special underwater drive unit.
Preferred embodiments of the sounding apparatus are defined in claims 2-9.
A method for carrying out a continuous sounding measurement according to the invention is defined in claim 10. In this case, the invention is based on a transfer principle. When the first clamping member, in the clamped position, ends a downwards movement, during which movement a sounding rod which is clamped in place by the first clamping members is pressed into a piece of ground, the second clamping members take over the penetration movement of the sounding rod, by likewise carrying out a downwards movement in the clamped position. At the same time as this latter step, the first clamping members, in the unclamped state, carry out an upwards movement. This results in a continuous penetration rate of the sounding rod. The continuous sounding measurement provides considerable advantages with regard to the quality and quantity of sounding measurements. Since the sounding can now be carried out on a continuous basis, considerable time can be saved. At a continuous penetration rate of 2 cm per second, a daily penetration depth to be measured of 200-250 m, and 50 working weeks per year, it is possible to save 100 hours per year. This provides a considerable cost saving. With regard to the quality of measurement, in practice it has been found that significantly better results are obtained. Advantageously, the measurement results show no trace of dissipation effects or of a build-up of skin friction. This allows measurements to be made more accurately and allows the soil properties to be determined over the entire penetration depth without interruption.